This invention relates to compositions derived from polyolefins combined with a polymeric nucleating agent. The nucleating agent is specifically a diene-propylene copolymer.
It is a common practice to use nucleating agents to increase the crystallization temperature (Tc) of polyolefins and/or to otherwise improve polyolefins by modifying their crystalline morphology. One reason for doing this is to increase melt processing efficiency and subsequent solid state strength-related properties. By increasing Tc, polyolefins crystallize or xe2x80x9cfreezexe2x80x9d at very near their melting temperature so that, for example, in molding processes, the polymer sets quickly after being injected into the mold.
There are many different types of nucleating agents used to increase the Tc of polyolefins. But because such agents are expensive and often impair other important polyolefin features, compounders and processors are constantly searching for nucleating agents that are economical and sufficiently increase Tc while not degrading other desirable polyolefin properties or introducing unwanted characteristics. The measurement of Tc is conveniently done utilizing differential scanning calorimetry (DSC) techniques.
Examples of common nucleating agents include inorganic substances such as talc, silicates, calcium carbonates, sodium phosphates, and stearates. Organic nucleating agents include polyesters, diacetals, dibenzylidene sorbitols, sodium benzoates, metal salts of carboxylic acids or alkyl-substituted derivatives thereof such as salts of stearic acids, adipic acid and sebacic acid, chromium p-tert-butyl benzoate and aluminum monophenyl acetate. Most common nucleating agent currently being used and recommended, specially for polypropylene family of polymers, are talc, sodium benzoate, and sorbitols.
We have discovered that diene-propylene copolymers serve as excellent nucleating agents for polyolefins, particularly propylene and ethylene based polyolefins.
In one embodiment the present invention is a polymer composition comprising a blend of: a) from 0.01 to 30 weight percent diene-propylene copolymer based on the total polymer composition weight; and b) crystallizable polyolefin comprising from a minimum of 0 to less than 100 percent by weight propylene derived units.
In another embodiment the present invention is a polymer composition comprising a blend of: a) from 0.01 to 10 weight percent diene-propylene copolymer based on the total polymer composition weight; and b) crystallizable polyolefin comprising at least 5% by weight ethylene derived units.
In another embodiment the present invention is a polymer composition obtained by blending: a) from 0.01 to 30 weight percent diene-propylene copolymer based on the total polymer composition weight; and b) at least 50 weight percent crystallizable polyolefin comprising at least 5% by weight ethylene derived units; wherein the polymer composition has a Tc at least 3xc2x0 C. greater than that of the crystallizable polyolefin alone.
In another embodiment one or more of the above compositions is prepared by combining the diene-propylene copolymer of a) with at least 50 weight percent of the crystallizable polyolefin of b) based on the total weight of the polymer composition.
In another embodiment one or more of the above blends has a Tc of at least 3xc2x0 C. greater than that of the crystallizable polyolefin alone.
In one or more of the above compositions the crystallizable polyolefin is selected from the group consisting of: syndiotactic propylene homopolymer, isotactic propylene-ethylene copolymers, syndiotactic propylene-ethylene copolymer, isotactic C4-C10 homopolymer, isotactic propylene-alpha olefin (C4-C18) copolymer, polyethylene homopolymer, polyethylene-ethylene alpha olefin (C4-C18) copolymers, propylene-ethylene-alpha olefin (C4-C18) terpolymers, and propylene impact copolymers.
In one or more of the above compositions the crystallizable polyolefin is selected from the group consisting of: isotactic propylene-ethylene copolymers, isotactic propylene-alpha olefin (C4-C18) copolymer, polyethylene homopolymer, ethylene alpha olefin (C4-C18) copolymers, propylene-ethylene-alpha olefin (C4-C18) terpolymers, and propylene impact copolymers.
In one or more of the above compositions the crystallizable polyolefin comprises at least 60 weight percent propylene derived units, and at least 5 weight percent ethylene derived units based on the total composition weight.
In one or more of the above compositions the crystallizable polyolefin comprises at least 80 weight percent propylene derived units based on the total composition weight.
In one or more of the above compositions the crystallizable polyolefin comprises at least 90 weight percent propylene derived units based on the total composition weight.
In one or more of the above compositions the crystallizable polyolefin comprises at least 95 weight percent propylene derived units based on the total composition weight.
In one or more of the above compositions the crystallizable polyolefin comprises an ethylene-propylene copolymer elastomer comprising 5 to 25% by weight ethylene-derived units and 95 to 75% by weight propylene-derived units, and has a melting point of less than 90xc2x0 C.
In one or more of the above compositions the crystallizable polyolefin has a heat of fusion of from 1.0 J/g to 37 J/g and a molecular weight distribution (Mw/Mn) of from 1.5 to 5.
One or more of the above compositions is prepared by combining from 0.15 to 10 weight percent of the diene-propylene copolymer of a) with the crystallizable polyolefin of b).
One or more of the above compositions is prepared by combining from 0.15 to 8 weight percent of the diene-propylene copolymer of a) with the crystallizable polyolefin of b).
One or more of the above compositions is prepared by combining from 0.15 to 5 weight percent of the diene-propylene copolymer of a) with the crystallizable polyolefin of b).
One or more of the above compositions is prepared by combining from 0.20 to 5 weight percent of the diene-propylene copolymer of a) with the crystallizable polyolefin of b).
In one or more of the above compositions the diene-propylene copolymer of a) comprises propylene derived units and from 0.001 to 2.0 weight percent diene derived units.
In one or more of the above compositions the diene-propylene copolymer of a) comprises propylene derived units and from 0.003 to 1.5 weight percent diene derived units.
In one or more of the above compositions the diene-propylene copolymer of a) comprises propylene derived units and from 0.005 to 1.0 weight percent diene derived units.
In one or more of the above compositions the diene-propylene copolymer of a) consists essentially of propylene derived units and from 0.01 to 2.0 weight percent diene derived units.